Laminated materials comprising a substrate and a layer of fibrillated cellulose are of particular interest since the layer of fibrillated cellulose imparts barrier properties to the substrate that are useful for packaging in particular.
Four types of processes are known for manufacturing such materials.
In one first process, known as the paper-making route, a very dilute suspension of cellulose (i.e. having a concentration of less than 5% by weight) is deposited on a web and a very dilute suspension of fibrillated cellulose is sprayed thereupon so that, after drainage through said web, a wet laminated fibrous web is obtained having a cellulose concentration in the order of 20% by weight, the layer of fibrillated cellulose having a lower concentration. The use of spraying, having regard to the speed of the machine, does not allow a very thick layer of fibrillated cellulose to be obtained once dried, the thickness generally being less than 3-5 μm.
In a second process used to manufacture cardboard, a very dilute suspension of cellulose is deposited on a web and, on an adjacent web, a very dilute suspension of fibrillated cellulose is deposited; drainage is caused to occur through each of the webs to obtain a fibrous web having a concentration of 10 to 15% by weight of cellulose, and the two webs are then assembled together. This process does not allow a thin layer of fibrillated cellulose to be obtained after drying, the thickness of the layer of fibrillated cellulose generally being greater than 15-20 μm.
The drainage of a suspension of fibrillated cellulose through a web is described in document WO 2013/171373.
In both these processes, the water content of the laminated fibrous web is reduced by means of a press that may be heated. One problem associated with this technique is that the layer of fibrillated cellulose adheres to the press, making handling difficult. Also, dehydration of said wet web is difficult to carry out.
In a third process known as a coating process, a suspension of fibrillated cellulose is coated onto the substrate to form a wet layer that is dried by infrared radiation (gas or electric), by convection (hot air) or conduction (in contact with a drying cylinder). However, for a concentration in the order of 2% by weight of fibrillated cellulose, the suspension has the consistency of a gel that is difficult to spread. To facilitate application of this suspension, the concentration of fibrillated cellulose must be reduced by increasing the amount of water. However, this increase in the water content deteriorates the properties of the fibrous substrate, makes it difficult to dry the layer of fibrillated cellulose and makes it difficult to obtain a sufficient layer thickness for the exhibiting of improved performance.
In a fourth process, a self-supporting film of fibrillated cellulose is produced as described in document WO 2013/060934 and is bonded by lamination onto a previously manufactured dry fibrous support material. This process does not allow narrow thicknesses of the layer of fibrillated cellulose to be obtained (less than 15 μm), since the fragility of thin films of fibrillated cellulose makes handling thereof difficult. Also, this technique requires the use of an adhesive to cause the self-supporting film to adhere to the fibrous support material. The laminated material thus obtained therefore comprises an adhesive layer.
Also, at the current time no process is known allowing a laminated material to be produced comprising a very thin layer of fibrillated cellulose (e.g. in the order of 3 to 20 μm), which in addition is also continuous and homogeneous.